The present invention relates to the removal of bran from cereal grains and milling of flour and/or semolina production. In particular, the present invention relates to a method and apparatus which subjects the grain kernels and particularly wheat kernels to process steps prior to subjecting them to the traditional tempering operation in preparation for milling.
The general objective of the milling process is to extract from the wheat kernel the maximum amount of endosperm in the purest form. The endosperm is either ground into flour or semolina. This requires the efficient separation of the components of the wheat kernels, namely the bran, endosperm, and germ. Bran and germ have a detrimental effect on the end milled products, flour or semolina.
In the conventional milling process, after the initial cleaning steps, the wheat kernels are conditioned with water and/or steam and allowed to rest in temper bins for 4 to 20 hours (tempering) to toughen the bran coats of the wheat kernels and soften or mellow the endosperm. Tempering of the wheat kernels fuses the bran coats together and is an essential conditioning step of the kernels carried out prior to the conventional milling process to alter the physical state of the kernels in a desired manner. Tempering is undoubtedly the most important factor in determining the amount of endosperm produced from given wheat kernels and, therefore, great care is taken to appropriately condition the kernels prior to milling.
The tempering of the wheat kernels to toughen and fuse the bran coats, unfortunately, also causes some fusion of the endosperm to the inner layers of bran whereby separation of these components is more difficult. The conditioned kernels are then subjected to successive stages, each of which grind, separate and purify the product. The first grinding operation (first break) opens the tempered kernels to expose the endosperm and scrape a portion of the endosperm from the bran. The coarsely ground mixture of bran, germ and endosperm particles is then sifted to classify the particles for further grinding, purification or sifting. The finer classified particles, which are a mixture of endosperm, bran and germ are then sent to the appropriate purification steps. The coarse remainder, consisting of bran and adhering endosperm, is sent to the next grinding step (second break) to remove more of the endosperm from the bran. The process of grinding, sifting and purification is repeated up to five or six times (5 or 6 breaks) in a conventional mill. However, each grinding process produces fine bran particles (bran powder) and germ particles which have a tendency to be separated with the endosperm and are difficult if not impossible, to remove from the endosperm. Each grinding operation produces more and more bran powder, compounding the problem.
Effective removal of the bran from the endosperm (flour and semolina) remains a problem affecting the yield possible from given wheat kernels at well as the fixed capital cost of a mill and the variable costs for milling high grade patent flour, and/or semolina.